This invention relates in general to bearings and more particularly to a process for setting bearings.
In many automotive vehicles of current manufacture the engine delivers its torque through a transmission to a drive shaft which, in turn, transmits the torque to a drive axle on which the driven wheels of the vehicle are mounted. Actually, the drive shaft couples with a pinion shaft that rotates in a differential housing which forms part of the drive axle. Here, a pinion on the pinion shaft, meshes with a ring gear, and the mesh of the two gears must be proper, lest the differential will generate excessive noise and wear rapidly. In order to achieve the proper mesh, the pinion shaft is mounted in the differential housing on a pair of tapered roller bearings which are set to a condition of preload so as to eliminate all axial and radial free motion between the shaft and the housing, while still allowing rotation with minimum friction within the housing.
The preload in the bearings imparts rigidity to the shaft, but too much preload will cause the bearings to overheat and fail prematurely. On the other hand, too little preload may cause the bearings to acquire end play, and this likewise decreases the life of the bearings and introduces radial and axial play into the shaft.
Under the current procedure for adjusting the bearings of a pinion shaft, a machine rotates the shaft relative to its housing and at the same time advances a nut which confines the inner races of the two bearings. As the nut advances, the bearings go from a condition of end play to preload. By monitoring the torque transmitted from the shaft to the housing, the machine determines the desired setting and, of course, terminates the advancement of the nut when the desired torque is achieved.
But torque does not always accurately reflect preload, and indeed like bearings which transmit the same torque may exist at different conditions of preload. For example, a tapered roller bearing with finely ground end faces on its rollers and a finely ground face on the thrust rib of its cone, requires a greater preload to exhibit the same torque as a more roughly ground bearing. Thus, the machine will set premium bearings at greater preload and perhaps cause the bearings to fail in service. By the same token, light machine oils will cause the bearings to transmit more torque than heavy gear oils at typical setting speeds so a pair of bearings set while lubricated with the latter may acquire too much preload force.
The process of the present invention, like the conventional procedure, causes a nut to advance over a pinion shaft to reduce the end play in a pair of bearings. Indeed, the process monitors the torque transmitted by the bearings as the nut is advanced and detects the point at which the bearings enter a condition of preload. At this point, the nut is rotated through a prescribed angle. Thus, the setting derived is purely dimensional in character and not subject to the variables which affect torque-dependent settings.